The present invention relates to brushless DC motors, and more particularly, to a brushless DC motor speed controller used for controlling the motor speed.
In conventional brushless DC motors, a DC tachometer or encoder is utilized as a speed sensor to achieve the purpose of speed control. In analog drivers to drive brushless DC motors, if a DC tachometer is utilized as the speed sensor, the feedback signal and the analog speed command enter the speed compensator concurrently. If an encoder is utilized as the speed sensor, the input signal is a pulse train, which is processed by a frequency-to-voltage converter to obtain an analog voltage. This analog voltage along with the analog speed command are then input to the speed compensator. When either of the aforementioned two methods is used for speed control, the brushless DC motor must be installed with a speed sensor. However, in certain applications such as drilling machines and automatic guided vehicles, in which speed control is required while large speed-fluctuation or slow response time is allowed, a simpler way of obtaining the speed feedback signal is feasible.